Image reading apparatus and image reading system

ABSTRACT

In an image sensor which has a photoelectric conversion element group, an illumination device having light sources of at least three emission colors R, G, and B, an imaging lens, and the like, moire noise in a color output image is eliminated, the original reading time is shortened, and a cost reduction is attained. For this purpose, a sensor array (1) including a linear array of a plurality of photoelectric conversion elements, a lens array (2) for imaging an original image on the sensor array (1), an illumination device (3) using LEDs having emission colors R, G, and B, and a cover glass (4) are supported by and fixed to a frame (5). The conjugate length of the lens array (2) is set to fall within the range between the B and G emission wavelengths. An original pressed against the cover glass (4) is illuminated by the illumination device (3), and light reflected by the original is converted into electrical signals by the sensor array (1), thereby reading the original image.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image reading apparatus forespecially reading a color original image and an image reading systemusing the same.

2. Related Background Art

FIG. 13 is a sectional view showing an example of an image sensor. Thissensor is constituted by a sensor array 1 which is prepared by mountinga sensor IC 101 on a sensor board 102, a lens array 2, an LED array 6having three different LED elements 301, 302, and 303 serving as lightsources for illuminating an original, a cover glass 4, and a frame 5 forholding these components in position.

The LED array 6 is constituted by mounting, on the board, a plurality ofthree different types of LED elements 301, 302, and 303, for example, 20or more elements on each line to obtain a uniform illuminancedistribution of an original upon reading an A4-size original.

The emission peak wavelengths of the three different LED elements 301,302, and 303 are respectively 430 (nm) corresponding to blue, 570 (nm)corresponding to green, and 660 (nm) corresponding to red.

The lens array 2 is formed by arranging a plurality of columnar lenselements on a line to provide a lens function by setting graduallydifferent refractive indices between the peripheral portion and thecentral portion.

Also, as the lens array 2, one having a small aperture angle is selectedangle since some color originals are adhered with pictures and havethree-dimensional patterns on their surface and, hence, a focal lengthof about 0.5 (mm) is required. Furthermore, a lens array 2 having smallchromatic aberrations is selected so that R, G, and B light beams canobtain substantially equal resolutions on the corresponding sensors.

In general, a lens array having an aperture angle of about 12 (deg.) isused, and a conjugate length (TC) as the distance between the originaland sensor requires 18.3 (mm).

However, since the above-mentioned conventional image sensor uses a lensarray with a small aperture angle, the light amount transmissionefficiency is low, and an increase in original reading speed is limited.

In addition, in the lens array with a small aperture angle, distancefrom the original surface to the sensor so long that size of the imagesensor using such the lens array becomes larger.

Furthermore, in the above-mentioned conventional image sensor, since thelens array equally inputs R, G, and B light beams onto the sensor array,a moire phenomenon appears, i.e., a very thin line in the read originalis output as a shaggy line in the output image. Such phenomenon isespecially conspicuous in a color original output image.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an image readingapparatus and system, which can complete reading within a short periodof time.

It is another object of the present invention to provide a compact,inexpensive image reading apparatus and system.

It is still another object of the present invention to eliminateproduction of moire noise upon reading a color image.

In order to achieve the above objects, according to one embodiment ofthe present invention, an image reading apparatus comprises: aphotoelectric conversion element; an illumination device having lightsources of first, second, and third colors having longer emissionwavelengths in the order named; an imaging member for imaging lightreflected by an original illuminated by the illumination device onto thephotoelectric conversion element; and a support member for supportingthe original, wherein an optical distance from a center of the imagingmember to the photoelectric conversion element is set at 1/2 of aconjugate length of light having a wavelength shorter than a peak valueof the emission wavelength of the light source of the third color, andan optical distance from the center of the imaging member to a surfaceof the original supported by the support member is set at 1/2 of aconjugate length of light of the emission wavelength having a conjugatelength shorter than the conjugate length.

According to another embodiment of the present invention, an imagereading system comprises: a photoelectric conversion element; anillumination device having light sources of first, second, and thirdcolors having longer emission wavelengths in the order named; an imagingmember for imaging light reflected by an original illuminated by theillumination device onto the photoelectric conversion element; a supportmember for supporting the original; and control means for controllingthe photoelectric conversion element and the illumination device,wherein an optical distance from a center of the imaging member to thephotoelectric conversion element is set at 1/2 of a conjugate length oflight having a wavelength shorter than a peak value of the emissionwavelength of the light source of the third color, and an opticaldistance from the center of the imaging member to a surface of theoriginal supported by the support member is set at 1/2 of a conjugatelength of light of the emission wavelength having a conjugate lengthshorter than the conjugate length.

According to still another embodiment of the present invention, an imagereading apparatus comprises: a photoelectric conversion element; anillumination device having light sources of first, second, and thirdcolors having longer emission wavelengths in the order named; an imagingmember for imaging light reflected by an original illuminated by theillumination device onto the photoelectric conversion element; and asupport member for supporting the original, wherein an optical distancefrom a center of the imaging member to the photoelectric conversionelement is set at 1/2 of a conjugate length at the emission wavelengthof the light source of the second color, and an optical distance fromthe center of the imaging member to a surface of the original supportedby the support member is set at 1/2 of a conjugate length at theemission wavelength of the light source of the first color.

According to still another embodiment of the present invention, an imagereading system comprises: a photoelectric conversion element; anillumination device having light sources of first, second, and thirdcolors having longer emission wavelengths in the order named; an imagingmember for imaging light reflected by an original illuminated by theillumination device onto the photoelectric conversion element; a supportmember for supporting the original; and control means for controllingthe photoelectric conversion element and the illumination device,wherein an optical distance from a center of the imaging member to thephotoelectric conversion element is set at 1/2 of a conjugate length atthe emission wavelength of the light source of the second color, and anoptical distance from the center of the imaging member to a surface ofthe original supported by the support member is set at 1/2 of aconjugate length at the emission wavelength of the light source of thefirst color.

With the above arrangement, the reading time can be shortened whilerealizing size and cost reductions of the reading apparatus and system.

According to still another embodiment of the present invention, an imagereading apparatus comprises: a photoelectric conversion element; anillumination device having light sources of first, second, and thirdcolors having longer emission wavelengths in the order named; and animaging member for imaging light reflected by an original illuminated bythe illumination device onto the photoelectric conversion element,wherein a conjugate length TC of the imaging member is set to satisfyA≦TC≦B where A is the conjugate length at the emission wavelength of thelight source of the first color, and B is the conjugate length at theemission wavelength of the light source of the second color.

According to still another embodiment of the present invention, an imagereading system comprises: a photoelectric conversion element; anillumination device having light sources of first, second, and thirdcolors having longer emission wavelengths in the order named; an imagingmember for imaging light reflected by an original illuminated by theillumination device onto the photoelectric conversion element; andcontrol means for controlling the photoelectric conversion element andthe illumination device, wherein a conjugate length TC of the imagingmember is set to satisfy A≦TC≦B where A is the conjugate length at theemission wavelength of the light source of the first color, and B is theconjugate length at the emission wavelength of the light source of thesecond color.

With the above-mentioned arrangement, a compact, inexpensive imagereading apparatus and system can be provided, and production of moireupon reading a color image can be eliminated.

Other objects and advantages of the present invention will becomeapparent from the following specification and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing the arrangement of an image sensor;

FIG. 2 is a top view showing the arrangement of the image sensor;

FIG. 3 is an enlarged sectional view of an illumination device shown inFIG. 1;

FIG. 4 is an enlarged side view of the illumination device shown in FIG.1;

FIG. 5 is a graph showing the spectral characteristics of the individuallight sources in the illumination device;

FIG. 6 is an explanatory view showing the imaging range of a lens arrayshown in FIG. 1;

FIG. 7 is a graph showing the chromatic aberration of the lens array;

FIG. 8 is an explanatory view showing the relationship between theconjugate length fluctuation and MTF in the lens array;

FIG. 9 is an explanatory view showing the focal depth characteristics ofthe lens array;

FIG. 10 is an explanatory view showing the R, G, and B focal depthcharacteristics;

FIG. 11 is a schematic sectional view showing the arrangement of aninformation processing apparatus using the image sensor;

FIG. 12 is a block diagram showing the arrangement of an informationprocessing system using the image sensor; and

FIG. 13 is a sectional view showing the arrangement of an image sensor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described hereinafterwith reference to the accompanying drawings.

FIGS. 1 and 2 are respectively a sectional view and a top view showingthe arrangement of an image sensor according to the present invention.This sensor is constituted by a sensor array 1 prepared by preciselyarranging sensor ICs 101 each having a linear array of a plurality ofphotoelectric conversion elements in a plurality of lines on, e.g., aglass epoxy sensor board 102 in correspondence with the length of theoriginal to be read, a lens array 2 for imaging light reflected by anoriginal onto the sensor array 1, an illumination device 3 forirradiating light onto an original, a cover glass 4 consisting of atransparent light transmission member for supporting an original, and aframe 5 which supports these components in position and consists of ametal such as aluminum or the like or a resin such as polycarbonate orthe like.

The mechanism of the sensor with the above-mentioned arrangement is asfollows. That is, the illumination device 3 selectively irradiatesthree, R, G, and B light beams in turn from an oblique direction ofabout 45° onto an original pressed against and supported by the coverglass 4, and the lens array 2 images three, R, G, and B opticalinformation signals reflected by the original onto the sensor IC 101.The sensor IC 101 photoelectrically converts the three, R, G, and Boptical information signals into electrical signals and supplies them toa system. The system processes the three, R, G, and B electrical signalsto reproduce a color image.

As shown in the enlarged views of FIGS. 3 and 4, the illumination device3 is made up of a three-color, RGB LED chip 31 which includes R, G, andB LED elements 311, 312 and 313 as light sources in a single package,and a light guide member 32 which guides light beams emitted by theseelements and outputs them in a desired direction, and uses a member suchas an acrylic resin having high light transmission characteristics.Also, in FIGS. 3 and 4, lead pins 314 are connected to the chip 31, andthe light guide member 32 has a sawtooth portion 321 and a projectingportion 322.

The peak emission wavelengths of the R, G, and B LED elements arerespectively selected to be 620 (nm), 530 (nm), and 470 (nm) so as toimprove color reproducibility and to reduce chromatic aberration as muchas possible. Note that these peak emission wavelengths need only fallwithin the ranges from 590 to 630 (nm), from 510 to 550 (nm), and 450 to490 (nm), respectively.

The LED chip 31 is arranged to input light from one edge portion in thelongitudinal direction of the light guide member 32 into the light guidemember 32, and the input light propagates inside the light guide member32 while repetitively undergoing total reflections at the interfacebetween the light guide member 32 and air.

As shown in FIGS. 3 and 4, the small-pitched sawtooth portion 321 isformed on the light guide member 32 to extend in its longitudinaldirection. Of light components that propagate inside the light guidemember, only light components entering the sawtooth portion 321 arelargely deflected toward the original surface unlike reflections atother surfaces, and cease to satisfy the total reflection condition atthe next interface between the light guide member 32 and air. In thismanner, such light components are output in a desired direction.

Such sawtooth portion 321 may be formed by a reflection surface preparedby depositing aluminum or printing silver ink, white ink, or the like,or using total reflections at the interface between the sawtooth shapeand air.

Alternatively, in place of forming a sawtooth shape, printing of whiteink or roughening of the surface may simply provide the same effect.

In order to easily obtain uniform illuminance on the original surface,the sawtooth portion 321 may be tapered wider as the distance from thelight source becomes larger, or the printed area may be graduallybroadened in the case of simple white ink printing.

Also, the light guide member 32 may be covered with, e.g., a whitemember with high light reflection efficiency except for a light outputportion toward the original, thus increasing the illuminance on theoriginal surface.

FIG. 5 shows the spectral characteristics of the light sources of theillumination device 3, i.e., the relationship between the R, G, and Bwavelengths (nm) and the relative emission intensities.

The lens array 2 used in this embodiment is formed by linearly aligninga plurality of columnar lens elements each having a diameter of 0.6 (mm)with high precision so as to provide a lens performance by settinghigher refractive indices from the peripheral potion toward the centralportion by, e.g., ion exchange.

FIG. 6 shows the imaging range of the lens array 2. The conventionalcolor image sensor has a maximum aperture angle θ=12 (deg.) since itconsists of a glass material suffering less chromatic aberration.However, the lens array 2 used in this embodiment can have an apertureangle θ=20 (deg.) or more since a glass material having proper chromaticaberration is selected.

As the aperture angle e becomes larger, the amount of light fetched bythe lens increases. For this reason, the light amount transmissionefficiency is improved, and the lens array 2 having an aperture angleθ=20 (deg.) provides brightness about four times that provided by theconventional sensor having θ=12 (deg.).

On the other hand, a conjugate length TC (the distance from the originalsurface to the sensor surface) is 18.3 (mm) in the lens array having theaperture angle θ=12 (deg.), while it is 9 (mm) in the lens array havingθ=20 (deg.).

FIG. 7 shows the chromatic aberration of the lens array 2. As shown inFIG. 7, the conjugate length TC (the distance from the original surfaceto the sensor surface) is varied to obtain maximum resolutions incorrespondence with the wavelengths of the light sources.

In this embodiment, as a light source, an R LED element having a peakwavelength λ=620 (nm) is selected, a G element having a peak wavelengthλ=530 (nm) is selected, and a B element having a peak wavelength λ=470(nm) is selected. For this reason, the conjugate lengths correspondingto maximum resolutions of these elements are respectively 9.4 (mm), 8.8(mm), and 8.2 (mm).

In this embodiment, the dimensions of the frame 5 and the cover glass 4are adjusted, so that an optical distance TC/2 between the sensor andthe lens center is set to be 4.4 mm half the conjugate length for the Gelement, an optical distance TC'/2 between the cover glass surface andthe lens center is set to be 4.1 (mm) half the conjugate length for theB element, and the total conjugate length TC is set at 8.5 (mm) nearlyequal to the middle length between those for the G and B elements.

However, these dimensions are selected under the assumption that theoptical path length of the lens is calculated based on air. However, ifglass (refractive index n=1.51) other than air is present in the opticalpath, the thickness of the glass must be set by multiplying the opticalpath length by the refractive index of the glass.

FIG. 8 shows changes in MTF (%) at 200 DPI when TC fluctuates, as thelens array characteristics of this embodiment. Also, FIG. 9 showschanges in MTF at 200 DPI owing to the difference between the opticaldistance TC/2 from the sensor to the lens center, and the opticaldistance TC'/2 from the original surface to the lens center. As can beseen from FIGS. 8 and 9, the highest MTF value can be obtained whenthese distances are equal to each other.

The R, G, and B focal depth characteristics shown in FIG. 10 are derivedfrom FIGS. 8 and 9 as those obtained when the cover glass surface ofthis embodiment is assumed to be 0.

The G and B depths of focus can assure an MTF value of 20% or more overa wide original surface position range of 0 to 0.5 (mm), and as for R, aresolution of 200 DPI can hardly be obtained at the original surfaceposition 0.

When a color original is read using three color LED elements, thecontrast of the dissected image is determined by the average of thethree colors. Hence, the edge portion of a very thin line isappropriately blurred by R, and an optimal color output image free fromany moire can be obtained.

Upon reading a monochrome original including many characters and thelike, when one or both of the G and B elements are turned on, and the Relement is turned off, even if the original slightly floats from thecover glass 4, an image having a required high resolution can beobtained.

In this embodiment, the conjugate length TC is adjusted just to thecenter of the conjugate lengths for G and B. Also, when the conjugatelength TC is adjusted to fall within the range between the conjugatelengths TC for G and B, i.e., to satisfy (TC for G)≧TC≧(TC for B), thesame effect as described above can be obtained.

The method of manufacturing the image sensor described above will beexplained below.

The lens array 2 and the illumination device 3 are respectively insertedat predetermined positions of the frame 5 shown in FIG. 1. Theillumination device 3 is inserted so that the three sides of the lightguide member 32 respectively abut against the horizontal and verticalsurfaces of the frame 5. In this manner, positioning in the rotationdirection of the optical axis can be precisely attained.

Subsequently, the cover glass 4 is adhered by, e.g., an adhesive, to twosurfaces, in the longitudinal direction, of the frame 5, which are setin approximately the same plane as the upper surfaces of the projectingportion 322 formed on a portion of the upper surface of the light guidemember 32, and the upper surface of the lens array 2, and which are setto sandwich the illumination device 3 and the lens array 2 therebetween.

When the frame 5 and the cover glass 4 are adhered to each other, thelens array 2 and the illumination device 3 can also be fixed in acluttering-free state.

Finally, the four lead pins 314 of the LED chip 31 are electricallyconnected to the sensor board by means of, e.g., soldering. In thismanner, the above-mentioned image sensor is completed.

FIG. 11 is a schematic sectional view showing the arrangement of aninformation processing apparatus using the above-mentioned image sensor.FIG. 11 exemplifies a printer for recording an image of an original PPon a recording medium P.

In FIG. 11, the apparatus includes an operation panel 20, a sensor unit100, a feed roller 102, platen rollers 106 and 112, a recording head110, a system control circuit board 130, a separation piece 140, and apower supply 150.

The overall control of this apparatus is made by a microcomputerarranged on the system control circuit board. Furthermore, themicrocomputer also performs control of the above-mentioned image sensor,i.e., ON/OFF control of the illumination device 3 and driving control ofthe sensor 1. An image signal read by the sensor unit 100 is subjectedto processing for recording onto the recording medium P or imageprocessing for externally outputting the image signal by a signalprocessing circuit on the system control circuit board 130. This signalprocessing circuit is also controlled by the microcomputer.

FIG. 12 shows an example of an information processing apparatusconstituted using the image sensor described in each of the aboveembodiments. In this example, an image reading apparatus 150 with abuilt-in image sensor 200 is connected to a personal computer 160 tobuild a system, and read image information is sent to a computer or ontoa computer network. This example will be explained below.

Referring to FIG. 12, the image reading apparatus 150 includes a CPU 170as a first control means for controlling the entire image readingapparatus 150, a color image sensor 200 which is made up of theabove-mentioned light sources, CCD line sensor, and the like, and servesas a reading unit for converting an original image into an image signal,and an analog signal processing circuit 116 for performing analogprocessing such as gain adjustment and the like for an analog imagesignal output from the color image sensor 200.

Also, the apparatus 150 includes an A/D converter 118 for converting theoutput from the analog signal processing circuit 116 into a digitalsignal, a digital image processing circuit 180 for performing imageprocessing such as shading correction, gamma conversion, variablemagnification processing, and the like for output data from the A/Dconverter 118 using a memory 122, and an interface 124 for outputtingdigital image data processed by the digital image processing circuit 180to an external apparatus. The interface 124 complies with standards suchas SCSI, Bi-Centronics, or the like, which are normally used in apersonal computer, and is connected to the personal computer 160. Theseanalog signal processing circuit 116, A/D converter 118, imageprocessing circuit 180, and memory 122 constitute a signal processingmeans.

The personal computer 160 serving as a second control means equips, asan external storage device or auxiliary storage device 132, amagnetooptical disk drive, a floppy disk drive, or the like. Thepersonal computer 160 includes a display 134 for displaying operationson the personal computer 160, and a mouse/keyboard 133 for inputtingcommands, and the like to the personal computer. Also, the personalcomputer 160 includes an interface 135 for exchanging data, commands,and status information of the image reading apparatus with the imagereading apparatus.

The personal CPU 136 of the computer 160 allows the user to input areading instruction to the CPU 170 of the image reading apparatus usingthe mouse/keyboard 133. When a reading instruction is input by themouse/keyboard 133, a CPU 136 transmits a reading command to the CPU 170of the image reading apparatus via the interface 135. The CPU 136 of thepersonal computer 160 controls the CPU 170 of the image readingapparatus in accordance with control program information stored in a ROM137, and the CPU 170 controls the light source, driving of the CCD andthe signal processing means. Note that this control program may bestored in a storage medium such as a magnetooptical disk, floppy disk,or the like loaded into the auxiliary storage device 132, and may beloaded into the personal computer 160 to be executed by the CPU 136.

In this manner, when the above-mentioned image sensor is used in thisapparatus, a practical, effective apparatus can be provided.

As described above, in an image sensor which comprises a photoelectricconversion element group for receiving light, an illumination device forirradiating three color light beams of first, second, and third colorsin turn from the shorter wavelength side, a lens for imaging lightreflected by an original on the photoelectric conversion element group,and the like, the conjugate length TC of the lens is set to satisfyA≦TC≦B where A is the conjugate length at the emission wavelength of alight source of the first color, and B is the conjugate length at theemission wavelength of a light source of the second color, whereby theresolution of light imaged on an R photoelectric conversion elementgroup is lower than those of G and B photoelectric conversion elementgroups, the edge portion of a very thin line in an output image uponreading the very thin line is appropriately blurred, and moire noiseespecially conspicuous in a color output image can be reduced, thusobtaining a high-quality image with optimal colors.

Upon reading a monochrome original which requires a high resolution forcharacters and the like, one or both of the G and B photoelectricconversion element groups are turned on, and the R photoelectricconversion element group is turned off, thus obtaining a desired image.Also, when the G and B photoelectric conversion element groups aresimultaneously turned on, the reading time can be shortened.

Since the R photoelectric conversion element group is not turned on, animage of a red stamp can be clearly seen, and the range of documentsthat can be processed is broadened.

Since a lens material having chromatic aberration can be used, a brightlens having an aperture angle of 20 (deg.) or more can be selected. Forthis reason, since the illuminance on the photoelectric conversionelement group can be increased, the S/N ratio can be improved, and thereading speed can be improved, thus achieving high performance.

Furthermore, since the illumination device is constituted by a lightsource and a light guide member for condensing light emitted by thelight source and outputting the condensed light in a desired direction,uniform illuminance on the original surface can be obtained by a smallernumber of light-emitting elements, thus realizing a great costreduction.

Also, in an image sensor which comprises a photoelectric conversionelement group for receiving light, an illumination device forirradiating three color light beams of first, second, and third colorsin turn from the shorter wavelength side, a lens for imaging lightreflected by an original on the photoelectric conversion element group,and the like, an optical distance between the photoelectric conversionelement group and the lens center is set at 1/2 of a conjugate length(TC) of light having a wavelength shorter than a peak value of theemission wavelength of the third color, and an optical distance betweenan original support surface of a cover member and the lens center is setat 1/2 of a conjugate length (TC') of light of the emission wavelengthhaving a conjugate length shorter than TC, whereby even when ashort-focal point, equal-magnification type lens array which has anaperture angle of 20 (deg.) or more and has a short depth of focus isused as the lens, depths of focus nearly equal to that of theconventional lens having an aperture angle of 12 (deg.) can be obtainedfor the individual colors, and a practically satisfactory output imagecan be obtained upon reading of an original adhered with a picture,which is often used in color image reading.

Since a short-focal point, equal-magnification type lens array having anaperture angle of 20 (deg.) can be used as a lens, the light amounttransmission efficiency for guiding light from an original toward thephotoelectric conversion element group can be improved, and the readingspeed of an original can be increased. Furthermore, since the conjugatelength (TC) is shortened, size reductions of the image sensor and theinformation processing apparatus using the same can be realized.

Furthermore, since the illumination device is constituted by a lightsource and a light guide member for condensing light emitted by thelight source and outputting the condensed light in a desired direction,uniform illuminance on the original surface can be obtained by a smallernumber of light-emitting elements, thus realizing a great costreduction.

Many widely different embodiments of the present invention may beconstructed without departing from the spirit and scope of the presentinvention. It should be understood that the present invention is notlimited to the specific embodiments described in the specification,except as defined in the appended claims.

What is claimed is:
 1. An image reading apparatus comprising:aphotoelectric conversion element; an illumination device having lightsources of first, second, and third colors having longer emissionwavelengths in the order named; an imaging member for imaging light froman original illuminated by said illumination device onto saidphotoelectric conversion element; and a support member for supportingthe original, wherein an optical distance from a center of said imagingmember to said photoelectric conversion element is set at 1/2 of a firstconjugate length of light having a wavelength shorter than a peak valueof the emission wavelength of the light source of the third color, andan optical distance from the center of said imaging member to a surfaceof the original supported by said support member is set at 1/2 of asecond conjugate length shorter than the first conjugate length, andwherein said photoelectric conversion element, said illumination device,said imaging member and said support member are held by a common holdmember.
 2. An apparatus according to claim 1, wherein a color originalis read by sequentially and selectively turning on three-color lightbeams of the first, second, and third colors.
 3. An apparatus accordingto claim 1, wherein when a monochrome original is read, light of thethird color or information based on the light of the third color is notused.
 4. An apparatus according to claim 3, wherein when a monochromeoriginal is read, at least one of the light sources of the emissionwavelengths of the first and second colors is turned on.
 5. An apparatusaccording to claim 1, wherein said imaging member comprises ashort-focal point, equal-magnification type rod lens having an apertureangle of not less than 20°.
 6. An apparatus according to claim 1,wherein said illumination device comprises a light guide member forguiding light from the light sources and outputting the light in adesired direction.
 7. An apparatus according to claim 1, wherein thelight sources use three different LEDs for respectively emitting first,second, and third light beams.
 8. An apparatus according to claim 1,wherein an emission peak wavelength of the first color falls within arange from 450 to 490 nm corresponding to blue, an emission peakwavelength of the second color falls within a range from 510 to 550 nmcorresponding to green, and an emission peak wavelength of the thirdcolor falls within a range from 590 to 630 nm corresponding to red. 9.An image reading apparatus comprising:a photoelectric conversionelement; an illumination device having light sources of first, second,and third colors having longer emission wavelengths in the order named;an imaging member for imaging light from an original illuminated by saidillumination device onto said photoelectric conversion element; and asupport member for supporting the original, wherein an optical distancefrom a center of said imaging member to said photoelectric conversionelement is set at 1/2 of a conjugate length at the emission wavelengthof the light source of the second color, and an optical distance fromthe center of said imaging member to a surface of the original supportedby said support member is set at 1/2 of a conjugate length at theemission wavelength of the light source of the first color, and whereinsaid photoelectric conversion element, said illumination device, saidimagine member and said support member are held by a common hold member.10. An apparatus according to claim 9, wherein a color original is readby sequentially and selectively turning on three-color light beams ofthe first, second, and third colors.
 11. An apparatus according to claim9, wherein when a monochrome original is read, light of the third coloror information based on the light of the third color is not used.
 12. Anapparatus according to claim 11, wherein when a monochrome original isread, at least one of the light sources of the emission wavelengths ofthe first and second colors is turned on.
 13. An apparatus according toclaim 9, wherein said imaging member comprises a short-focal point,equal-magnification type rod lens having an aperture angle of not lessthan 20°.
 14. An apparatus according to claim 9, wherein saidillumination device comprises a light guide member for guiding lightfrom the light sources and outputting the light in a desired direction.15. An apparatus according to claim 9, wherein the light sources usethree different LEDs for respectively emitting first, second, and thirdlight beams.
 16. An apparatus according to claim 9, wherein an emissionpeak wavelength of the first color falls within a range from 450 to 490nm corresponding to blue, an emission peak wavelength of the secondcolor falls within a range from 510 to 550 nm corresponding to green,and an emission peak wavelength of the third color falls within a rangefrom 590 to 630 nm corresponding to red.
 17. An image reading apparatuscomprising:a photoelectric conversion element; an illumination devicehaving light sources of first, second, and third colors having longeremission wavelengths in the order named; and an imaging member forimaging light from an original illuminated by said illumination deviceonto said photoelectric conversion element, wherein a conjugate lengthTC of said imaging member is set to satisfy A≦TC≦B where A is theconjugate length at the emission wavelength of the light source of thefirst color, and B is the conjugate length at the emission wavelength ofthe light source of the second color, and wherein said photoelectricconversion element, said illumination de vice and said imaging memberare held by a common hold member.
 18. An apparatus according to claim17, wherein a color original is read by sequentially and selectivelyturning on three-color light beams of the first, second, and thirdcolors.
 19. An apparatus according to claim 17, wherein when amonochrome original is read, light of the third color or informationbased on the light of the third color is not used.
 20. An apparatusaccording to claim 19, wherein when a monochrome original is read, atleast one of the light sources of the emission wavelengths of the firstand second colors is turned on.
 21. An apparatus according to claim 17,wherein said imaging member comprises a short-focal point,equal-magnification type rod lens having an aperture angle of not lessthan 20°.
 22. An apparatus according to claim 17, wherein saidillumination device comprises a light guide member for guiding lightfrom the light sources and outputting the light in a desired direction.23. An apparatus according to claim 17, wherein the light sources usethree different LEDs for respectively emitting first, second, and thirdlight beams.
 24. An apparatus according to claim 17, wherein an emissionpeak wavelength of the first color falls within a range from 450 to 490nm corresponding to blue, an emission peak wavelength of the secondcolor falls within a range from 510 to 550 nm corresponding to green,and an emission peak wavelength of the third color falls within a rangefrom 590 to 630 nm corresponding to red.
 25. An image reading systemcomprising:a photoelectric conversion element; an illumination devicehaving light sources of first, second, and third colors having longeremission wavelengths in the order named; an imaging member for imaginglight from an original illuminated by said illumination device onto saidphotoelectric conversion element; a support member for supporting theoriginal; and control means for controlling said photoelectricconversion element and said illumination device, wherein an opticaldistance from a center of said imaging member to said photoelectricconversion element is set at 1/2 of a first conjugate length of lighthaving a wavelength shorter than a peak value of the emission wavelengthof the light source of the third color, and an optical distance from thecenter of said imaging member to a surface of the original supported bysaid support member is set at 1/2 of a second conjugate length shorterthan the first conjugate length, and wherein said photoelectricconversion element, said illumination device, said imagine member andsaid support member are held by a common hold member.
 26. A systemaccording to claim 25, wherein a color original is read by sequentiallyand selectively turning on three-color light beams of the first, second,and third colors.
 27. A system according to claim 25, wherein when amonochrome original is read, light of the third color or informationbased on the light of the third color is not used.
 28. A systemaccording to claim 27, wherein when a monochrome original is read, atleast one of the light sources of the emission wavelengths of the firstand second colors is turned on.
 29. A system according to claim 25,wherein said imaging member comprises a short-focal point,equal-magnification type rod lens having an aperture angle of not lessthan 20°.
 30. A system according to claim 25, wherein said illuminationdevice comprises a light guide member for guiding light from the lightsources and outputting the light in a desired direction.
 31. A systemaccording to claim 25, wherein the light sources use three differentLEDs for respectively emitting first, second, and third light beams. 32.A system according to claim 25, wherein an emission peak wavelength ofthe first color falls within a range from 450 to 490 nm corresponding toblue, an emission peak wavelength of the second color falls within arange from 510 to 550 nm corresponding to green, and an emission peakwavelength of the third color falls within a range from 590 to 630 nmcorresponding to red.
 33. An image reading system comprising:aphotoelectric conversion element; an illumination device having lightsources of first, second, and third colors having longer emissionwavelengths in the order named; an imaging member for imaging light froman original illuminated by said illumination device onto saidphotoelectric conversion element; a support member for supporting theoriginal; and control means for controlling said photoelectricconversion element and said illumination device, wherein an opticaldistance from a center of said imaging member to said photoelectricconversion element is set at 1/2 of a conjugate length at the emissionwavelength of the light source of the second color, and an opticaldistance from the center of said imaging member to a surface of theoriginal supported by said support member is set at 1/2 of a conjugatelength at the emission wavelength of the light source of the firstcolor, and wherein said photoelectric conversion element, saidillumination device, said imaging member and said support member areheld by a common hold member.
 34. A system according to claim 33,wherein a color original is read by sequentially and selectively turningon three-color light beams of the first, second, and third colors.
 35. Asystem according to claim 33, wherein when a monochrome original isread, light of the third color or information based on the light of thethird color is not used.
 36. A system according to claim 35, whereinwhen a monochrome original is read, at least one of the light sources ofthe emission wavelengths of the first and second colors is turned on.37. A system according to claim 33, wherein said imaging membercomprises a short-focal point, equal-magnification type rod lens havingan aperture angle of not less than 20°.
 38. A system according to claim33, wherein said illumination device comprises a light guide member forguiding light from the light sources and outputting the light in adesired direction.
 39. A system according to claim 33, wherein the lightsources use three different LEDs for respectively emitting first,second, and third light beams.
 40. A system according to claim 33,wherein an emission peak wavelength of the first color falls within arange from 450 to 490 nm corresponding to blue, an emission peakwavelength of the second color falls within a range from 510 to 550 nmcorresponding to green, and an emission peak wavelength of the thirdcolor falls within a range from 590 to 630 nm corresponding to red. 41.An image reading system comprising:a photoelectric conversion element;an illumination device having light sources of first, second, and thirdcolors having longer emission wavelengths in the order named; an imagingmember for imaging light from an original illuminated by saidillumination device onto said photoelectric conversion element; andcontrol means for controlling said photoelectric conversion element andsaid illumination device, wherein a conjugate length TC of said imagingmember is set to satisfy A≦TC≦B where A is the conjugate length at theemission wavelength of the light source of the first color, and B is theconjugate length at the emission wavelength of the light source of thesecond color, and wherein said photoelectric conversion element, saidillumination device and said imaging member are held by a common holdmember.
 42. A system according to claim 41, wherein a color original isread by sequentially and selectively turning on three-color light beamsof the first, second, and third colors.
 43. A system according to claim41, wherein when a monochrome original is read, light of the third coloror information based on the light of the third color is not used.
 44. Asystem according to claim 43, wherein when a monochrome original isread, at least one of the light sources of the emission wavelengths ofthe first and second colors is turned on.
 45. A system according toclaim 41, wherein said imaging member comprises a short-focal point,equal-magnification type rod lens having an aperture angle of not lessthan 20°.
 46. A system according to claim 41, wherein said illuminationdevice comprises a light guide member for guiding light from the lightsources and outputting the light in a desired direction.
 47. A systemaccording to claim 41, wherein the light sources use three differentLEDs for respectively emitting first, second, and third light beams. 48.A system according to claim 41, wherein an emission peak wavelength ofthe first color falls within a range from 450 to 490 nm corresponding toblue, an emission peak wavelength of the second color falls within arange from 510 to 550 nm corresponding to green, and an emission peakwavelength of the third color falls within a range from 590 to 630 nmcorresponding to red.